1. Field of the Invention
The invention relates to lithography, and more particularly to a method of reworking a photoresist layer to replace a collapsed photoresist layer.
2. Description of the Related Art
As semiconductor manufacturers have sought to fabricate devices with a higher degree of circuit integration to improve device performance, it has become necessary to use photolithography with shorter wavelengths in the mid and deep UV spectra to achieve fine features. In the process of making the desired very fine patterns, many optical effects are experienced which lead to distortion or displacement of images in the photoresist that are directly responsible for wiring line width variations, opens, and shorts, all of which can lead to deteriorated device performance. Many of these optical effects are attributable to substrate geometry and reflectivity influences that include halation and other reflected light scattering effects which may occur due to uneven topography or the varying (wavelength dependent) reflectivity of the substrates and wires or layers being patterned thereon to define the desired features. Such effects are further exacerbated by both the non-uniformity of the photoresist film and film thickness. These effects are manifested in lithographic patterns; uneven line width, often with “reflective notching”, due to standing wave phenomena, and non-vertical pattern side walls. Therefore, the application of an anti-reflect coating (ARC) layer has been developed to impede reflection of the light source and solve standing wave phenomena.
In order to define very fine patterns, such as shallow trenches and contacts, the aspect ratio of the patterns of a photoresist layer is getting higher.
However, collapse problems frequently occur in a photoresist layer due to the high aspect ratio of the patterns. Thus, a reworked photoresist layer is formed after the collapsed photoresist layer is removed by ashing, comprising introducing oxygen-containing plasma to the collapsed photoresist layer. Because the plasma also reacts with the anti-reflect layer, some acids are produced thereon, leading to undercutting in the reworked photoresist layer following formation on the anti-reflect layer.